Anomalous resistivity and thermopower of the spinel-type compoundsCuIr2S4and

А. Т. Бурков

¹

,

Takao Nakama

²

,

Masato Hedo

³

et al.

Abstract

Resistivity () and thermopower ͑S͒ of spinel-type compounds CuIr 2 S 4 and CuIr 2 Se 4 have been measured at temperatures from 2 to 900 K under magnetic field from 0 to 15 T. The thermopower is positive in the metallic phase of both compounds at high temperatures, as well as in the low-temperature insulating state of CuIr 2 S 4 . The positive thermopower of the insulating phase implies p-type charge carriers, in agreement with the recent photoemission results. The low-temperature resistivity of CuIr 2 S 4 is in good agreement with the Efros-Shklovskii variable-range hopping conductivity mechanism: ϭ 0 exp͓(T*/T) 1/2 ͔. The most striking result is that the resistivity of the metallic phases is well described by an exponential-type temperature dependence in a wide temperature range from 2 K to at least 900 K. This unusual result for metals type of the resistivity temperature dependence, as well as other features in the transport properties, imply a nonconventional conductivity mechanism. The magnetoresistivity ⌬ is positive and proportional to H 2 , while magnetothermopower ⌬SϭS(H,T)ϪS(0,T) is very small for both compounds at all temperatures.

Ir5dstate ofCuIr2S4:Kitamoto1, Taguchi2, Mimura3 et al. 2003Phys. Rev. B11240View full textAdd to dashboardCite

“…7 The electrical conductivity of CuIr 2 S 4 below 50 K has been described by the Efros-Shklovskii hopping with long-range Coulomb correlation. 8,9 It is considered that the correlation effect among the Ir 5d electrons in CuIr 2 S 4 plays an important role in the charge-order transition, although the electronic states of 5d transition-metal compounds have not been usually described by the localized picture. Matsuno et al have investigated both occupied and unoccupied electronic structures of CuIr 2 S 4 using PES and bremsstrahlung isochromat spectroscopy ͑BIS͒.…”

Detailed Mapping of the LocalIr4+Dimers through the Metal-Insulator Transitions ofCuIr2S4Thiospinel by X-Ray Atomic P

“…It has a nonconventional conduction mechanism [22] and a recent observation of weak Fermi edges and broad peak features in ultraviolet photoemission spectra suggest that fluctuating dimers may survive in the high temperature metallic phase [23]. A PDF study can address this directly since the PDF is sensitive to the existence of the dimers whether or not they are ordered [23].…”

Diamagnetism in spinel compound

“…Ir 5de orbitals, mainly deðxyÞ, also play a main role for conductivity. The conductivity in the insulating phase (LIP) is proportional to exp ½ÀðT à =TÞ 1=2 [5]. Further, it has been observed that a change of the lattice symmetry from triclinic to tetragonal symmetry, preserving the local triclinic structure, can be induced by X-ray or electron beam irradiation at Tp50 K [10,11].…”

“…The physical properties of CuIr 2 S 4 thiospinel compound with temperature-induced metal-insulator transition (MIT) observed at the transition temperature T MI ¼ 230 K [1][2][3][4][5][6] has been intensively studied. The transition is of the first order, accompanied by volume reduction of about 0:7% at T MI in a low-temperature insulating phase (LIP) compared to that in a high-temperature metallic phase (HMP).…”